Diverse communities broaden ecosystem function




  • Species occur together
    • not all perfectly adapted
    • networks of trophic interactions
    • ecosystems work better as a group


  • Ecosystems work better as a group
    • No single species performs all roles
    • larger threshold of environmental conditions
    • fosters ecosystem resilience (ball & cup model)

Diverse communities broaden ecosystem function




  • Species occur together
    • not all perfectly adapted
    • networks of trophic interactions
    • ecosystems work better as a group


  • Ecosystems work better as a group
    • No single species performs all roles
    • larger threshold of environmental conditions
    • fosters ecosystem resilience (ball & cup model)

Not all species are created equal


Reintroduction of wolves in Yellowstone: Top down control


Hierarchical levels in an community: Food webs


Energy flow limits length of food chain (10% rule)


Building ecosystems: Succession


Disturbance & succession


Disturbance



  • Discrete event in time that:
    • Removes biomass
    • alters populations & communities
    • alters structure of ecosystems
    • changes resources availability
    • changes physical environment


  • Natural vs Human caused disturbance
    • lightning, herbivory, flood
    • mining, clear-cutting


  • Maintains communities in non-equilibrium

Severity of disturbance: intensity and size



Severity of natural disturbances: frequency



Primary succession





  • After severe disturbances
    • remove or bury biomass
    • no soil


  • Glacial retreat, mud-flows, floodplains, lava flows


  • Colonization:
    • species that handle stresses
    • low nutrients / minimal soil

Primary succession: Facilitators





  • Initial Species composition:
    • nitrogen fixers
    • Facilitation


  • Colonizers must disperse to site
    • wind dispersed seeds/spores
    • algae & lichens
    • small seeded plants
    • distance matters

Secondary succession


Secondary succession: pioneer species






  • Potential growth rate:


  • Tolerance:


  • Seed size & Number:


  • Longevity:

Late succession: inhibition & tolerance


Wildlife and succession


The Boreal: forests shaped by fire


Boreal forest succesion: Aspen - Spruce - Cedar


The future of boreal forests


Study aid: Glacier Bay Alaska succession